The invention concerns an extraction means for producing coffee for a coffee machine.
An extraction means is described in EP-B-0 299 399. It incorporates an adjustable brewing cylinder for receiving coffee powder working in co-operation with a drive means that is reciprocably moveable along a longitudinal guide between pre-determined positions as well as two pistons, adjustable relative to one another and positioned coaxially in relation to the brewing cylinder. The coffee powder is inserted through a side filler opening of the brewing cylinder, whereby an end of the brewing cylinder, which is open at the front, is held closed by one of the two pistons, i.e. the substantially fixedly installed first piston. During the adjusting of the brewing cylinder in one direction, via the first piston, the first piston defines a front-side brewing chamber together with the second piston that is moved by the brewing cylinder and ensures compression of the inserted coffee powder. In this position boiling water is inserted into the brewing chamber through one piston and pumped through the compressed coffee powder, whereafter the coffee produced in this way is conveyed to an outlet of the coffee machine through the other piston. During the subsequent adjusting of the brewing cylinder in the other direction the used coffee powder is ejected through the second piston from the brewing cylinder end that has in the meantime been released by the first piston.
Another coffee extraction means according to publication U.S. Pat. No. 5,275,089 also envisages two pistons that can be adjusted in relation to the brewing cylinder and a block incorporating a filler opening for the insertion of coffee powder. On the inside of this cylinder shaped block a sleeve and one piston are located and can be moved in a longitudinal direction. In the filling position this block is positioned at the rear sleeve part and abuts against the front side of the same together with the other piston, whereas the same are separate from one another in the ejection position. In the brewing position the piston that is positioned near the additional part comes to rest inside the cylinder part. As this sleeve within the block is a necessary requirement and has to be displaceable just like the piston associated with the same, the construction of this extraction means is complicated.